Question

the phone company nextfell has a monthly cellular plan where a customer pays a flat monthly fee and then a certain amount of money per minute used on the phone. if a customer uses 390 minutes, the monthly cost will be $69. if the customer uses 770 minutes, the monthly cost will be $107. a) find an equation in the form y = mx + b, where x is the number of monthly minutes used and y is the total monthly of the nextfell plan. answer: y = do not use any commas in your answer. b) use your equation to find the total monthly cost if 926 minutes are used. answer: if 926 minutes are used, the total cost will be dollars.

Explanation:

Step1: Find the slope $m$

We have two points $(x_1,y_1)=(390,69)$ and $(x_2,y_2)=(770,107)$. The slope formula is $m=\frac{y_2 - y_1}{x_2 - x_1}$. So $m=\frac{107 - 69}{770 - 390}=\frac{38}{380}=0.1$.

Step2: Find the y - intercept $b$

Use the point - slope form $y - y_1=m(x - x_1)$ with the point $(390,69)$ and $m = 0.1$. So $y-69=0.1(x - 390)$. Expand it: $y-69=0.1x-39$. Then $y=0.1x + 30$.

Step3: Find the cost for 926 minutes

Substitute $x = 926$ into the equation $y=0.1x + 30$. So $y=0.1\times926+30=92.6+30=122.6$.

Answer:

A. $y = 0.1x+30$
B. 122.6